fix: add error handling and validation

[amnonbc]

Summary

This PR addresses critical bugs and improves error handling and data validation across the DRM and framebuffer backends.

Changes

Critical Bug Fixes:

• drm.Flip(): Now properly handles ioctl errors. Previously, errors were silently ignored, causing the active buffer pointer to be updated even when the hardware flip failed, leading to subsequent frames rendering to the wrong buffer.
• drm.Open(): Standardized error cleanup paths to consistently use the cleanup function instead of scattered f.Close() calls, ensuring all resources are properly released.

Data Safety Improvements:

• fb.Blit() and fb.Flip(): Added bounds validation to catch image size mismatches before blitting. Provides clear error logging when callers pass incorrectly-sized images.
• fb.Open(): Added integer overflow protection when calculating framebuffer size. Added sanity check to reject unreasonably large allocations (>256MB).

Readability Enhancements:

• Added detailed comments explaining Bayer matrix indexing (y&3, x&3) in blitToHardware()
• Improved documentation for setPlaneRotation() about failure modes

Testing

All changes are backward compatible. The validation checks will catch invalid inputs that would have previously caused panics or undefined behavior.

Issues Addressed

• Fixes potential data corruption in DRM backend when flip operations fail
• Prevents undersized image buffers from causing memory access violations
• Protects against integer overflow in framebuffer size calculation